1. Field of the Invention
This invention relates generally to systems for identifying the features that contribute to the cardiac performance of an individual patient through the use of imaging methods, and in particular to a computerized system and method for facilitating and assessing cardiac intervention methods.
2. Description of the Related Art
The circulatory system of a human works as a closed system where the effects of one part of the system are felt by all other parts of the system. For example, if a person's blood pressure rises then there is a corresponding pressure decrease in the venous system, the decrease is much smaller than the increase in the arterial side because of the fact that venous vasculature is more compliant than the arterial vasculature. Within the circulatory system the key component is the heart. Any change to any component of the heart will have an effect felt throughout the entire system.
The function of a heart in an animal is primarily to deliver life-supporting oxygenated blood to tissue throughout the body. This function is accomplished in four stages, each relating to a particular chamber of the heart. Initially deoxygenated blood is received in the right auricle of the heart. This deoxygenated blood is pumped by the right ventricle of the heart to the lungs where the blood is oxygenated. The oxygenated blood is initially received in the left auricle of the heart and ultimately pumped by the left ventricle of the heart throughout the body. It may be seen that the left ventricular chamber of the heart is of particular importance in this process as it pumps the oxygenated blood through the aortic valve and ultimately throughout the entire vascular system.
A myocardial infarction (i.e., a heart attack) will not affect two people in the same manner. The extent of the damage due to the infarction will be based on many factors, such as; location of the infarction, extent of collateral flow in the blockage area, health of the heart prior to infarction, etc. The unique damage will have a corresponding unique effect on the entire cardiac system. The infarction damage in one patient may be isolated to a small section of the ventricle wall. In another person, the infarction may involve not only the ventricle wall but also the septum. In still another person, the infarction might involve the papillary muscles. Over time, these unique damages will cause the heart to respond in different ways in an attempt to keep the circulatory system operating optimally.
Various treatments are currently employed to repair, replace or mitigate the effects of damaged components of the heart. Some of these treatments involve grafting new arteries onto blocked arteries, repairing or replacing valves, reconstructing a dilated left ventricle, administering medication or implanting mechanical devices. All these treatments apply standard repairs to unique problems with a minimum of analysis as to what the optimum intervention should involve. Typically, the current procedures do not involve analyzing the performance of the cardiac system after the treatment to see what effect the treatment has had on the entire system. For example, a patient with blocked arteries may undergo a standard treatment of placing 5-6 grafts on their heart due solely to a short visual inspection of angiographic films that show some stenosis of the arteries of the heart. No analysis is performed to see if placing 3-4 grafts will achieve the same perfusion of the myocardium as the 5-6 grafts. It is simply a situation where the physician decides that more is better, which may not be true. Placing 5-6 grafts requires more surgical time, longer pump runs, and incisions into numerous areas of the body to recover the needed grafts. This increases morbidity to the patient and may contribute to death of the patient who may not tolerate the additional stress of a longer, more invasive procedure. On some patients, the extra grafts may be needed, since collateral flow, or flow from other arteries, is not sufficient to perfuse the entire myocardium. On other patients, the grafts may not be needed, since sufficient flows will be generated from fewer grafts. Currently, the physician has no way of knowing if the total number of grafts that he put in was appropriate.
A similar procedure is used to place stents in a vessel. Stents are placed in vessels based on an assessment of blockage and ability to access the obstructed area. No method of analysis is performed to determine the effects of placing a stent, to analyze how many stents should be placed, or to determine if the placement of stents produces a better result than bypassing.
The current process for repairing and replacing valves heavily relies on the physician's knowledge and intuition. There is no precise way to determine how much a valve or structural component needs to change or what the effect of that change will be. The current procedure for determining if the correct repair was made is to complete the repair, remove the patient from cardiopulmonary bypass and let the heart start beating. When the heart's performance reaches a normal range, an echocardiography is taken of the valve to ensure that it is not regurgitant. If the repair left some regurgitation, then the patient must go back on cardiopulmonary bypass, the heart must be stopped again, reopened, and additional repair work must be performed. This checking procedure is repeated after the second repair to ensure that the procedure has been correctly done. This procedure subjects the patient to unnecessary risks by exposing them to longer than necessary bypass runs and reperfusion injuries each time the heart is weaned of cardioplegia. This procedure also takes up valuable operating room and staff time. This multiple repair scenario for valve procedures is typical for most patients. Additionally, this assessment method only assesses one factor related to the performance of the valve and ventricle, regurgitation. A physician may perform a procedure, which corrects the existing problem, but creates another problem or diminishes the performance of the ventricle. The physician has little, if any, way to know if he compromised ventricle performance, since current analytical tools only look for flow across the valve. It would be desirable to have available methods to identify and evaluate the positioning of the valve apparatus, the attached tissue, and their combined performance.
Similarly, it would be desirable to have improved methods to determine when to replace or repair a valve. Typically, this is left to the judgment of the physician based on a review of two-dimensional echocardiography studies. Physicians who are unfamiliar with repair techniques may opt for replacement when repair is not only possible but also the best course of action for the patient. Typically, a valve replacement will be done without knowing what effect it will have on the other elements of the mitral valve apparatus, left ventricle, left atrium and the overall functioning of the heart. For example, a replacement that attaches the chordae tendinae to the new valve may have a much different effect on the ventricle than a replacement that excludes the chordae tendinae. It would be useful to have a method to assist the physician in making this assessment. Repairs are typically undertaken to shorten the chordae and annulus without knowing what effect the repairs will have on the entire apparatus. The current solution is to make the repair and let the heart beat to see what the repair has done.
What is needed, therefore, is a reliable method and apparatus to allow a physician to determine which elements of the heart are not contributing to, or are decrementing from, the performance of the heart. It is also desirable to have a method and apparatus to allow the physician to simulate the treatment on a portion of those elements and see the effect the treatment has on the other elements and the heart as a whole prior to performing the surgery.